Battery diagnostic device, battery diagnostic method, battery diagnostic program, and vehicle

ABSTRACT

A battery diagnostic device includes an acquisition unit that acquires a temperature and an internal resistance of a battery; a determination unit that determines a diagnostic temperature that is a temperature used for a diagnosis of the battery, based on the temperature acquired by the acquisition unit; an estimation unit that estimates the internal resistance of the battery at the diagnostic temperature based on the temperature and the internal resistance acquired by the acquisition unit and the diagnostic temperature determined by the determination unit; and a diagnosis unit that diagnoses the battery based on the internal resistance estimated by the estimation unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of application Ser. No. 17/157,036,filed Jan. 25, 2021, which claims priority to Japanese PatentApplication No. 2020-054865, filed on Mar. 25, 2020. The contents of theprior applications are hereby incorporated by reference in theirentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a battery diagnostic device and thelike for diagnosing a battery mounted on a vehicle.

2. Description of Related Art

Batteries (secondary batteries) such as lithium ion batteries arediagnosed based on internal resistance. In this regard, JapaneseUnexamined Patent Application Publication No. 2010-236925 (JP2010-236925 A) discloses a technique that acquires the temperature andthe resistance value of the secondary battery, estimates the internalresistance value of the secondary battery at a specific temperaturebased on a predetermined model, and uses the internal resistance valuefor performance diagnosis at the temperature.

SUMMARY

When the difference between the temperature of the secondary batterywhen the internal resistance is acquired and the temperature used fordiagnosis is relatively large, the estimation accuracy of the estimatedvalue of the internal resistance at the temperature used for thediagnosis may decrease due to an internal resistance acquisition errorwhen estimating the internal resistance based on the model, and thediagnostic accuracy of the performance diagnosis may also decrease.

An object of the present disclosure is to provide a battery diagnosticdevice having high diagnostic accuracy.

An aspect of the present disclosure for solving the above issue is abattery diagnostic device including: an acquisition unit that acquires atemperature and an internal resistance of a battery; a determinationunit that determines a diagnostic temperature that is a temperature usedfor a diagnosis of the battery, based on the temperature acquired by theacquisition unit; an estimation unit that estimates the internalresistance of the battery at the diagnostic temperature based on thetemperature and the internal resistance acquired by the acquisition unitand the diagnostic temperature determined by the determination unit; anda diagnosis unit that diagnoses the battery based on the internalresistance estimated by the estimation unit.

According to the present disclosure, it is possible to improve theestimation accuracy of the internal resistance and thus improve thediagnostic accuracy of the battery by determining the temperature usedfor the diagnosis based on the temperature of the battery and using itfor estimating the internal resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a configuration diagram of a vehicle control system accordingto an embodiment;

FIG. 2 is a diagram showing an example of power supply control accordingto the embodiment;

FIG. 3 is a diagram showing an example of the power supply controlaccording to the embodiment;

FIG. 4 is a diagram showing an example of discharge control according tothe embodiment;

FIG. 5 is a functional block diagram of a battery diagnostic deviceaccording to the embodiment;

FIG. 6 is a flowchart showing an example of a battery diagnostic processaccording to the embodiment;

FIG. 7 is a diagram showing an example of a discharge pattern of thebattery diagnostic process according to the embodiment;

FIG. 8 is a diagram showing an example of a measurement sample accordingto the embodiment; and

FIG. 9 is a flowchart showing an example of a battery diagnosticsub-process according to the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS Embodiment

In a battery diagnostic device according to an embodiment of thetechnique described in the present disclosure, for example, a differentdiagnostic temperature is determined for each assumed temperature changepattern based on the temperature of the battery to be diagnosed and isused for estimating the internal resistance, which improves theestimation accuracy. This can improve the reliability of batterydiagnosis.

Configuration

FIG. 1 is a diagram showing a configuration example of a vehicle controlsystem 1 mounted on a vehicle 200 according to an embodiment of thetechnique described in the present disclosure.

A main battery 11, a high voltage battery 12, and a directcurrent-to-direct current (DC-DC) converter 13 constitute a main powersupply system. The main battery 11 is, for example, a lead acid battery.

A sub-battery 21 constitutes a sub-power supply system. The sub-powersupply system is a backup system to be used in case of a failure of themain power supply system described above. A heater 22 can raise thetemperature of the sub-battery 21. The sub-battery 21 is, for example, alithium ion battery.

An SBW ACT 14 is an actuator that controls the shift position, and inparticular, can set the shift position to the parking position toperform parking lock. An SBW ECU 15 is an electronic control unit (ECU)that controls the SBW ACT 14. The SBW ECU 15 controls the SBW ACT 14 toelectrically control the shift position (shift-by-wire control).

An ADS ECU 23 is an ECU that executes the function of the automateddriving system.

A power supply control device 100 includes a bidirectional DC-DCconverter 101, a power supply control unit 102, and a battery diagnosticdevice 110, and can control power supply to the actuator and the ECUsdescribed above and can perform performance diagnosis of the sub-battery21. Each function of the power supply control unit 102 and the batterydiagnostic device 110 is executed by a control unit including aprocessor and a memory. The number of control units is not limited, andeach function of the power supply control unit 102 and the batterydiagnostic device 110 may be executed by one control unit or may beexecuted individually by different control units.

The vehicle control system 1 may include various ECUs and actuators inaddition to those described above.

Here, an example of control of the power supply control device 100 willbe described. The power supply control unit 102 of the power supplycontrol device 100 monitors values of a current sensor and a voltagesensor (not shown) provided in each part of the vehicle control system 1to detect whether the main power supply system is normal or has failed,and appropriately controls a plurality of switches such as relays (notshown) appropriately provided inside and outside of the power supplycontrol device 100 to perform the following power supply control.

FIG. 2 shows an example of the power supply control during autonomousdriving when the main power supply system operated by the power supplycontrol unit 102 is normal. In this case, the power supply control unit102 supplies the output power of the main battery 11 and the outputpower of the high voltage battery 12 whose voltage has been stepped downby the DC-DC converter 13 to the SBW ACT 14, the SBW ECU 15, the ADS ECU23, and the like.

The temperature of the sub-battery 21 is measured by a temperaturesensor (not shown) provided in the sub-battery 21. When the temperatureof the sub-battery 21 is lower than a first temperature T1 and equal toor higher than a second temperature T2 that is lower than the firsttemperature T1, the power supply control unit 102 supplies the outputpower of the sub-battery 21 to the heater 22 and raises the temperatureof the sub-battery 21 to improve power characteristics of thesub-battery 21 such as the voltage and a state of charge. When thetemperature of the sub-battery 21 is lower than the second temperature,the power characteristics cannot be expected to be sufficiently improvedbased on the temperature rise of the sub-battery 21, so that the outputpower of the sub-battery 21 is not supplied to the heater 22 and thetemperature of the sub-battery 21 is not raised. The power supplycontrol unit 102 may appropriately supply the output power of the mainbattery 11 or the high voltage battery 12 to the sub-battery 21 via thebidirectional DC-DC converter 101 to charge the sub-battery 21. Further,the power supply control unit 102 applies the output voltage of thesub-battery 21 to the ADS ECU 23, but controls the bidirectional DC-DCconverter 101 to suppress the power supply from the sub-battery 21.

FIG. 3 shows an example of the power supply control performed by thepower supply control unit 102 when the main power supply system failsduring autonomous driving. In this case, the power supply control unit102 supplies the output power of the sub-battery 21 to the SBW ACT 14,the SBW ECU 15, the ADS ECU 23, and the like. The power supply from thesub-battery 21 to the heater 22 is performed in the same manner asdescribed above. In this state, the ADS ECU 23 performs limp homecontrol for stopping the vehicle 200 promptly and safely, and after thevehicle 200 stops, the SBW ACT 14 and the SBW ECU 15 perform the parkinglock. Even when the main power supply system fails during manualdriving, the power supply control unit 102 supplies the output power ofthe sub-battery 21 to the SBW ACT 14 and the SBW ECU 15, and after thevehicle 200 stops, the SBW ACT 14 and the SBW ECU 15 perform the parkinglock.

FIG. 4 shows an example of discharge control for acquiring internalresistance by the battery diagnostic device 110. The battery diagnosticdevice 110 appropriately controls a plurality of switches such as relays(not shown) appropriately provided inside and outside of the powersupply control device 100, and discharges power from the sub-battery 21while restricting a discharge voltage and a discharge current by thebidirectional DC-DC converter 101. The discharged power is appropriatelyconsumed by the load of the ECUs, the actuators, and the like.

Diagnostic Process

FIG. 5 shows a functional block diagram of the battery diagnostic device110. The battery diagnostic device 110 includes an acquisition unit 111,a determination unit 112, an estimation unit 113, and a diagnosis unit114.

The acquisition unit 111 acquires the temperature and the internalresistance of the sub-battery 21. The determination unit 112 determinesthe diagnostic temperature, which is the temperature used for thediagnosis of the sub-battery 21, based on the temperature acquired bythe acquisition unit 111. The estimation unit 113 estimates the internalresistance of the sub-battery 21 at the diagnostic temperature based onthe temperature and the internal resistance acquired by the acquisitionunit 111 and the diagnostic temperature determined by the determinationunit 112. The diagnosis unit 114 diagnoses the sub-battery 21 based onthe internal resistance estimated by the estimation unit 113.

FIG. 6 shows a flowchart of the battery diagnostic process performed bythe battery diagnostic device 110, and the process will be describedaccording to the flowchart. This process is executed at a timing beforethe vehicle starts traveling, before other operations of the vehiclecontrol system 1 are started, and when the power discharge of thesub-battery 21 can be relatively stably performed, such as a timingimmediately after the ignition is turned on (power on).

Step S101

When the ignition is turned on, the acquisition unit 111 dischargespower from the sub-battery 21 as described above. FIG. 7 shows anexample of a pattern of a discharge current and a discharge voltage. Theacquisition unit 111 measures a current I1 and a voltage V1 before thestart of discharge with the current sensor and the voltage sensor. Asshown in FIG. 7, the discharge is performed with a constant current anda constant voltage for a certain period of time. The acquisition unit111 measures the current I2 and the voltage V2 in a state where thedischarge current and the discharge voltage are stable.

Step S102

The acquisition unit 111 acquires the internal resistance of thesub-battery 21. The internal resistance can be derived based on thecurrent and voltage samples (I1, V1) and (I2, V2) measured at two timepoints. FIG. 8 shows a graph that maps two samples. If there is no errorin the values of the two samples, the internal resistance is theabsolute value R′ of the inclination of the straight line passingthrough the two samples in the graph, but the current sensor and thevoltage sensor have measurement errors. The true values corresponding tothe two samples fall within a range of the measurement error withrespect to the sample. In FIG. 8, for example, the ranges surrounded bydotted lines indicate the ranges in which the true value exists for eachsample when the current and the voltage respectively have measurementerrors of ±Ie and ±Ve. However, since the current I1 is the currentbefore the start of discharge, the true value can be specified as zero.

In general, the larger the internal resistance is, the lower theperformance of the sub-battery 21 is. Thus, it is not preferable thatthe internal resistance is evaluated to be smaller than the true value.In view of this, the maximum value that the internal resistance can takewhen the current value and the voltage value fall within such a range isderived as the internal resistance to be acquired. In the example shownin FIG. 8, the absolute value of the inclination of the straight linepassing through the two points (0, V1+Ve) and (I2−Ie, V2−Ve) is definedas the internal resistance R.

In this way, the acquisition unit 111 corrects the absolute value R′ ofthe rate of change in the voltage with respect to the current when thedischarge is performed to a larger value R based on the measurementaccuracy of the current and the voltage, and acquires the value of R asthe internal resistance. As described above, the corrected internalresistance R may be derived based on the existence range of the truevalue, and may be derived by multiplying R′ by a coefficient α (>1)appropriately determined based on the assumed range of the measuredvalues of the current and the voltage and the measurement accuracy.

Step S103

The acquisition unit 111 acquires the temperature and the state ofcharge (SOC) of the sub-battery 21. Here, the acquisition unit 111acquires the measured value of the temperature sensor as the temperatureT. Further, the acquisition unit 111 derives an open circuit voltage(OCV) based on the voltage V1 before discharging power from thesub-battery 21, and refers to a map defining in advance the relationshipbetween the OCV and the SOC, and acquires SOC1 that is the SOCcorresponding to the derived OCV.

Step S104

The determination unit 112 determines the diagnostic temperature Td,which is the temperature used for the diagnosis, as follows based on themagnitude relationship between the above-mentioned temperature T, thefirst temperature T1, and the second temperature T2, as illustrated inFIG. 9.

When T≥T1 holds, Td=T1 (S104 a).When T1>T≥T2 holds, Td=T (S104 b).When T2>T holds, Td=T3 (S104 c).Here, T3 represents a third temperature T3 that is lower than the secondtemperature T2. The third temperature T3 is the guaranteed minimumtemperature of the sub-battery 21, which is a temperature substantiallylow enough that there is no need to assume that the sub-battery 21functions below this temperature.

As described below, the diagnostic temperature Td can be regarded as thelowest value that the temperature can take in the temperature changepattern of the sub-battery 21 that is assumed based on the temperature Tacquired by the acquisition unit 111.

As described above, when the temperature of the sub-battery 21 is lowerthan T1 and equal to or higher than T2, the temperature is raised by theheater 22 as described above (S104 d). Therefore, the following holds.

When T≥T1 holds, even if the temperature of the sub-battery 21subsequently decreases, the temperature of the sub-battery 21 does notbecome lower than T1.When T1>T≥T2 holds, the temperature of the sub-battery 21 issubsequently raised by the heater 22 and does not become lower than T.When T2>T holds, even if the temperature of the sub-battery 21subsequently decreases, it is not necessary to assume that thetemperature becomes lower than T3, and T3 may be regarded as the minimumvalue.

Generally, the internal resistance of the sub-battery 21 increases asthe temperature decreases. Thus, if the SOC of the sub-battery 21 is thesame, the diagnostic temperature Td is a temperature when the internalresistance of the sub-battery 21 becomes the largest while the vehicleis traveling. In the present embodiment, the determination unit 112appropriately sets the diagnostic temperature Td in this way based onthe temperature T acquired by the acquisition unit 111.

Step S105

The estimation unit 113 estimates the internal resistance of thesub-battery 21 at the diagnostic temperature Td. The estimation isperformed by referring to a map defining in advance the relationshipbetween the temperature and the internal resistance, and deriving theinternal resistance Rd when the temperature T of the sub-battery 21acquired by the acquisition unit 111 changes to the diagnostictemperature Td. An example of this map is shown below. Numerical valuesin the map are omitted as appropriate.

TABLE 1 Internal resistance (mΩ) Temperature . . . . . . . . . . . . . .. (° C.) 25 . . . 1.0 1.5 . . . . . . . . . . . . . . . . . . T1 . . .4.0 6.0 . . . . . . . . . . . . . . . . . . T3 . . . 15.0  22.5  . . .

When the temperature T of the sub-battery 21 acquired by the acquisitionunit 111 is 25° C. and the internal resistance R is 1.0 mΩ, referring tothe map, when the diagnostic temperature Td is T1, the internalresistance Rd is 4.0 mΩ. The internal resistance Rd when the diagnostictemperature Td is T3 is 15.0 mΩ.

The internal resistance R may include an error with respect to the truevalue even when the above correction is performed. For example, assumingthat the diagnostic temperature Td is always the guaranteed minimumtemperature T3, the error of the internal resistance Rd increases evenwith a slight error as shown in the map. For example, when thetemperature T is 25° C., the error of the internal resistance R is 0.5mΩ (=1.5 mΩ-1.0 mΩ), but the error of the internal resistance at thetemperature T3 is 7.5 mΩ (=22.5 mΩ-15.0 mΩ), and the error increases.

Further, for example, when the diagnostic temperature Td is always theguaranteed minimum temperature T3, the internal resistance of thesub-battery 21 is evaluated larger than necessary in the assumedtemperature change pattern of the sub-battery 21.

For example, when the temperature T is 25° C., the temperature will notbe lower than the temperature T1, so that the maximum value of theinternal resistance can be reliably evaluated with the internalresistance at the temperature T1. Further, when the temperature T is 25°C. and the error of the internal resistance R is 0.5 mΩ (=1.5 mΩ-1.0mΩ), the error of the internal resistance at the temperature T1 is 2.0mΩ (=6.0 mΩ-4.0 mΩ), and the error can be further suppressed than thatof the internal resistance at the temperature T3.

In the present embodiment, by appropriately setting the diagnostictemperature Td based on the acquired temperature T of the sub-battery21, the difference between the diagnostic temperature Td and thetemperature T can be suppressed, and the internal resistance of thesub-battery 21 can be estimated by suppressing errors andoverestimation.

Step S106

The diagnosis unit 114 diagnoses the sub-battery 21 based on theestimated internal resistance Rd. For example, it is diagnosed whetherthe voltage of the sub-battery 21 can become lower than the voltage Vminat which quality deterioration occurs. The voltage at which qualitydeterioration occurs is determined by the product of the permissiblelower limit voltage of the cells constituting the sub-battery 21 and thenumber of serial layers thereof.

The voltage of the sub-battery 21 decreases the most after themeasurement by the acquisition unit 111 and when the main power supplysystem fails while the vehicle is traveling, so that the sub-battery 21discharges a power amount W required for satisfying the condition forperforming limp home control and the subsequent parking lock, and theSOC is reduced from the SOC1 by the amount corresponding to the poweramount W. Assuming that the SOC after the decrease is SOCd used for thediagnosis, the OCV in SOCd is OCVd, the internal resistance is Rd′, andthe current required for performing the parking lock is Id, when Rd′ isequal to or lower than Rmax that satisfies the following equation, itcan be diagnosed that the voltage of the sub-battery 21 does not becomelower than Vmin and the condition imposed on the sub-battery 21 can besatisfied without causing quality deterioration.

OCVd−Id×R max=V min

i.e., R max=(OCVd−V min)/Id

Here, OCVd in SOCd can be acquired by referring to a map defining inadvance the relationship between the OCV and the SOC. Further, theinternal resistance Rd′ in SOCd is acquired by referring to a mapdefining in advance the relationship between the SOC and the internalresistance and by deriving the change in the internal resistance from Rdin a case where the SOC of the sub-battery 21 acquired by theacquisition unit 111 changes from SOC1 to SOCd. An example of this mapis shown below. Numerical values in the map are omitted as appropriate.

TABLE 2 State of charge (SOC) (%) . . . SOCd . . . SOC1 . . .Temperature . . . . . . . . . . . . . . . . . . (° C.) T . . . R4 . . .R1 . . . . . . . . . . . . . . . . . . . . . T1 . . . R5 . . . R2 . . .. . . . . . . . . . . . . . . . . . T3 . . . R6 . . . R3 . . .

This map shows that, for example, at a temperature T, when the SOC isSOC1 and the internal resistance is R1, the internal resistance changesto R4 when the SOC changes to SOCd. Using this map, when the internalresistance is Rd when the SOC is SOC1 at the temperature T, the internalresistance in SOCd is calculated by Rd×R4/R1.

That is, the internal resistance Rd′ when the diagnostic temperatureTd=T and the SOC is SOCd can be obtained by the following equation.

Rd′=Rd×R4/R1

Similarly, the internal resistance Rd′ when the diagnostic temperatureTd=T1 and the SOC is SOCd can be obtained by the following equation.

Rd′=Rd×R5/R2

Similarly, the internal resistance Rd′ when the diagnostic temperatureTd=T3 and the SOC is SOCd can be obtained by the following equation.

Rd′=Rd×R6/R3

When the Rd′ obtained in this way is equal to or lower than Rmax, asdescribed above, it can be diagnosed that the voltage of the sub-battery21 is not lower than Vmin and the condition can be satisfied withoutcausing quality deterioration. If the condition is not satisfied, forexample, the user may be notified by a warning light or the like, oreven if the main power supply system fails, the vehicle may travel onlyin a limp home mode and the parking lock may be manually performed bythe user.

Effect

As described above, in the battery diagnostic device according to theembodiment of the technique described in the present disclosure, forexample, a different diagnostic temperature is determined for eachassumed temperature change pattern based on the temperature of thebattery to be diagnosed and is used for estimating the internalresistance, which improves the estimation accuracy. This can improve thereliability of battery diagnosis. It should be noted that the techniquedescribed in the present disclosure can be applied to cases other thanthe above embodiment as long as the diagnostic temperature for thecurrent battery temperature can be determined based on at least one ofthe battery characteristics, control specifications such ascharge/discharge and temperature rise/cooling, and usage environmentsuch as ambient air temperature.

Although the embodiment of the technique described in the presentdisclosure has been described above, the technique described in thepresent disclosure can be construed as a battery diagnostic device, abattery diagnostic method executed by a battery diagnostic deviceincluding a processor and a memory, a battery diagnostic program forexecuting a battery diagnostic method, a computer-readablenon-transitory storage medium that stores a battery diagnostic program,a vehicle control system including a battery diagnostic device, andvehicle equipped with a battery diagnostic device.

INDUSTRIAL AVAILABILITY

The technique described in the present disclosure can be applied to abattery diagnostic device of a vehicle and the like.

What is claimed is:
 1. A battery diagnostic device comprising: anacquisition unit that acquires a temperature and an internal resistanceof a battery; a determination unit that determines a diagnostictemperature that is a temperature used for a diagnosis of the battery,based on the temperature acquired by the acquisition unit; an estimationunit that estimates the internal resistance of the battery at thediagnostic temperature based on the temperature and the internalresistance acquired by the acquisition unit and the diagnostictemperature determined by the determination unit; and a diagnosis unitthat diagnoses the battery based on the internal resistance estimated bythe estimation unit, wherein the acquisition unit further acquires astate of charge of the battery when acquiring the temperature and theinternal resistance of the battery, and the diagnosis unit: derives,based on the internal resistance and the state of charge acquired by theacquisition unit, the internal resistance assumed when the batterydischarges a power amount specified by a given condition from the stateof charge acquired by the acquisition unit, and diagnoses that thebattery satisfies the condition when the internal resistance that isderived is equal to or lower than the internal resistance in which thevoltage assumed in a case where the battery discharges the power amountwith the current specified by the condition is the voltage specified bythe condition.
 2. The battery diagnostic device according to claim 1,wherein the determination unit determines a minimum temperature in atemperature change pattern of the battery that is assumed based on thetemperature acquired by the acquisition unit as the diagnostictemperature.
 3. The battery diagnostic device according to claim 2,wherein: when the temperature of the battery is lower than a firsttemperature and equal to or higher than a second temperature that islower than the first temperature, temperature rise control is performedon the battery with heat supplied from an outside; and the determinationunit determines the first temperature as the diagnostic temperature whenthe temperature acquired by the acquisition unit is equal to or higherthan the first temperature, determines the temperature acquired by theacquisition unit as the diagnostic temperature when the temperatureacquired by the acquisition unit is lower than the first temperature andequal to or higher than the second temperature, and determines a thirdtemperature that is lower than the second temperature as the diagnostictemperature when the temperature acquired by the acquisition unit islower than the second temperature.
 4. The battery diagnostic deviceaccording to claim 1, wherein the internal resistance acquired by theacquisition unit is derived based on a current and a voltage of thebattery measured at two time points.
 5. The battery diagnostic deviceaccording to claim 1, wherein the acquisition unit acquires a currentand a voltage of the battery, corrects an absolute value of a rate ofchange in the voltage with respect to the current to a larger valuebased on an acquisition accuracy of the current and an acquisitionaccuracy of the voltage, and regards the absolute value that has beencorrected as an acquired value of the internal resistance.
 6. Thebattery diagnostic device according to claim 1, wherein the state ofcharge is derived from an open circuit voltage based on a voltageacquired by the acquisition unit before power is discharged from thebattery and a predetermined relationship between open circuit voltageand state of charge.
 7. A battery diagnostic method comprising: anacquisition step of acquiring a temperature and an internal resistanceof a battery; a determination step of determining a diagnostictemperature that is a temperature used for a diagnosis of the battery,based on the temperature acquired in the acquisition step; an estimationstep of estimating the internal resistance of the battery at thediagnostic temperature based on the temperature and the internalresistance acquired in the acquisition step and the diagnostictemperature determined in the determination step; and a diagnosis stepof diagnosing the battery based on the internal resistance estimated inthe estimation step, wherein the acquisition step includes acquiring astate of charge of the battery when acquiring the temperature and theinternal resistance of the battery, and the diagnosis step includes:deriving, based on the internal resistance and the state of chargeacquired in the acquisition step, the internal resistance assumed whenthe battery discharges a power amount specified by a given conditionfrom the state of charge acquired in the acquisition step, anddiagnosing that the battery satisfies the condition when the internalresistance that is derived is equal to or lower than the internalresistance in which the voltage assumed in a case where the batterydischarges the power amount with the current specified by the conditionis the voltage specified by the condition.
 8. The battery diagnosticmethod according to claim 7, wherein the determination step includesdetermining a minimum temperature in a temperature change pattern of thebattery that is assumed based on the temperature acquired in theacquisition step as the diagnostic temperature.
 9. The batterydiagnostic method according to claim 8, wherein: when the temperature ofthe battery is lower than a first temperature and equal to or higherthan a second temperature that is lower than the first temperature,temperature rise control is performed on the battery with heat suppliedfrom an outside; and the determination step includes: determining thefirst temperature as the diagnostic temperature when the temperatureacquired in the acquisition step is equal to or higher than the firsttemperature, determining the temperature acquired in the acquisitionstep as the diagnostic temperature when the temperature acquired in theacquisition step is lower than the first temperature and equal to orhigher than the second temperature, and determining a third temperaturethat is lower than the second temperature as the diagnostic temperaturewhen the temperature acquired in the acquisition step is lower than thesecond temperature.
 10. The battery diagnostic method according to claim7, wherein the internal resistance acquired in the acquisition step isderived based on a current and a voltage of the battery measured at twotime points.
 11. The battery diagnostic method according to claim 7,wherein the acquisition step includes acquiring a current and a voltageof the battery, correcting an absolute value of a rate of change in thevoltage with respect to the current to a larger value based on anacquisition accuracy of the current and an acquisition accuracy of thevoltage, and regarding the absolute value that has been corrected as anacquired value of the internal resistance.
 12. The battery diagnosticmethod according to claim 7, wherein the state of charge is derived froman open circuit voltage based on a voltage acquired in the acquisitionstep before power is discharged from the battery and a predeterminedrelationship between open circuit voltage and state of charge.
 13. Anon-transitory computer readable storage medium having stored therein abattery diagnostic program to be executable by a computer, the programcausing the computer to execute: an acquisition step of acquiring atemperature and an internal resistance of a battery; a determinationstep of determining a diagnostic temperature that is a temperature usedfor a diagnosis of the battery, based on the temperature acquired in theacquisition step; an estimation step of estimating the internalresistance of the battery at the diagnostic temperature based on thetemperature and the internal resistance acquired in the acquisition stepand the diagnostic temperature determined in the determination step; anda diagnosis step of diagnosing the battery based on the internalresistance estimated in the estimation step, wherein the acquisitionstep includes acquiring a state of charge of the battery when acquiringthe temperature and the internal resistance of the battery, and thediagnosis step includes: deriving, based on the internal resistance andthe state of charge acquired in the acquisition step, the internalresistance assumed when the battery discharges a power amount specifiedby a given condition from the state of charge acquired in theacquisition step, and diagnosing that the battery satisfies thecondition when the internal resistance that is derived is equal to orlower than the internal resistance in which the voltage assumed in acase where the battery discharges the power amount with the currentspecified by the condition is the voltage specified by the condition.14. The non-transitory computer readable storage medium according toclaim 13, wherein the determination step includes determining a minimumtemperature in a temperature change pattern of the battery that isassumed based on the temperature acquired in the acquisition step as thediagnostic temperature.
 15. The non-transitory computer readable storagemedium according to claim 14, wherein: when the temperature of thebattery is lower than a first temperature and equal to or higher than asecond temperature that is lower than the first temperature, temperaturerise control is performed on the battery with heat supplied from anoutside; and the determination step includes: determining the firsttemperature as the diagnostic temperature when the temperature acquiredin the acquisition step is equal to or higher than the firsttemperature, determining the temperature acquired in the acquisitionstep as the diagnostic temperature when the temperature acquired in theacquisition step is lower than the first temperature and equal to orhigher than the second temperature, and determining a third temperaturethat is lower than the second temperature as the diagnostic temperaturewhen the temperature acquired in the acquisition step is lower than thesecond temperature.
 16. The non-transitory computer readable storagemedium according to claim 13, wherein the internal resistance acquiredin the acquisition step is derived based on a current and a voltage ofthe battery measured at two time points.
 17. The non-transitory computerreadable storage medium according to claim 13, wherein the acquisitionstep includes acquiring a current and a voltage of the battery,correcting an absolute value of a rate of change in the voltage withrespect to the current to a larger value based on an acquisitionaccuracy of the current and an acquisition accuracy of the voltage, andregarding the absolute value that has been corrected as an acquiredvalue of the internal resistance.
 18. The non-transitory computerreadable storage medium according to claim 13, wherein the state ofcharge is derived from an open circuit voltage based on a voltageacquired in the acquisition step before power is discharged from thebattery and a predetermined relationship between open circuit voltageand state of charge.
 19. A vehicle including the battery diagnosticdevice according to claim
 1. 20. A vehicle including the batterydiagnostic device according to claim 3.